PIC12F1822-ISLASHMF datasheet(219/398 Pages) MICROCHIP

219 / 398 page

 2010 Microchip Technology Inc.

Preliminary

DS41413A-page 219

PIC12F/LF1822/16F/LF1823

23.4.6.1

Steering Synchronization

The STR1SYNC bit of the PSTR1CON register gives

the user two selections of when the steering event will

happen. When the STR1SYNC bit is ‘0’, the steering

event will happen at the end of the instruction that

writes to the PSTR1CON register. In this case, the

output signal at the output pins may be an incomplete

PWM waveform. This operation is useful when the user

firmware needs to immediately remove a PWM signal

from the pin.

When the STR1SYNC bit is ‘1’, the effective steering

update will happen at the beginning of the next PWM

period. In this case, steering on/off the PWM output will

always produce a complete PWM waveform.

Figures 23-19 and 23-20 illustrate the timing diagrams

of the PWM steering depending on the STR1SYNC

setting.

23.4.7

START-UP CONSIDERATIONS

When any PWM mode is used, the application

hardware must use the proper external pull-up and/or

pull-down resistors on the PWM output pins.

The CCP1M<1:0> bits of the CCP1CON register allow

the user to choose whether the PWM output signals are

active-high or active-low for each pair of PWM output

pins (P1A/P1C and P1B/P1D). The PWM output

polarities must be selected before the PWM pin output

drivers

are

enabled.

Changing

the

polarity

configuration while the PWM pin output drivers are

enable is not recommended since it may result in

damage to the application circuits.

The P1A, P1B, P1C and P1D output latches may not be

in the proper states when the PWM module is

initialized. Enabling the PWM pin output drivers at the

same time as the Enhanced PWM modes may cause

damage to the application circuit. The Enhanced PWM

modes must be enabled in the proper Output mode and

complete a full PWM cycle before enabling the PWM

pin output drivers. The completion of a full PWM cycle

is indicated by the TMR2IF bit of the PIR1 register

being set as the second PWM period begins.

FIGURE 23-19:

EXAMPLE OF STEERING EVENT AT END OF INSTRUCTION (STR1SYNC = 0)

FIGURE 23-20:

EXAMPLE OF STEERING EVENT AT BEGINNING OF INSTRUCTION

(STR1SYNC = 1)

Note:

When the microcontroller is released from

Reset, all of the I/O pins are in the high-

impedance state. The external circuits

must keep the power switch devices in the

Off state until the microcontroller drives

the I/O pins with the proper signal levels or

activates the PWM output(s).

PWM

P1n = PWM

STR1

P1<D:A>

PORT Data

PWM Period

PORT Data

PWM

PORT Data

P1n = PWM

STR1

P1<D:A>

PORT Data

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